Coulibaly Fasséli
Structural Virology laboratory, School of Biomedical Sciences, Monash University, Clayton, VIC3800, Australie.
Virologie (Montrouge). 2012 Jun 1;16(3):134-147. doi: 10.1684/vir.2012.0449.
Viral polyhedroses are very common diseases of insects. They were first identified as leading causes of losses in the silk industry. This heterogeneous group of diseases is characterized by the formation of crystals in infected cells that are called viral polyhedra or occlusion bodies and represent the infectious form of the viruses. Polyhedra have similar role in the infectious cycle of the two groups of viruses responsible for polyhedroses, the cypoviruses - members of the Reoviridae family - and the Baculoviridae. Polyhedra embed virus particles within infected cells in a robust crystalline matrix that protects viral infectivity after release in the environment. Upon ingestion by a new host, crystals dissolve readily thereby releasing the infectious particles to initiate a new viral cycle. Owing to their unique molecular organization, these atypical infectious forms have long intrigued virologists and biochemists alike. They attracted particular interest because of the in vivo crystallization process and the contrast between rapid release upon ingestion and extreme stability. It is only recently that novel approaches and technologies allowed the structure determination of such tiny crystals by X-ray crystallography. Cypovirus and baculovirus polyhedra share the same role in the virus cycle, the same crystalline lattice with a cubic centered symmetry, and matrix proteins called polyhedrins of similar sizes. However, their building blocks differ by their folds and packing in polyhedra. The two classes of polyhedra therefore harbour distinct molecular architectures and appear to have emerged independently in the virosphere. The role of tyrosine clusters in polyhedra dissolution and the use of molecular arms to achieve in vivo crystallization may thus represent striking cases of convergent evolution. This review summarizes our understanding of viral polyhedra with an emphasis on the recent structural studies. We also provide examples of biotechnological applications entailing structure-based engineering of polyhedra as novel types of crystalline microparticules.
病毒多角体病是昆虫非常常见的疾病。它们最初被确定为丝绸行业损失的主要原因。这类异质性疾病的特征是在受感染细胞中形成晶体，这些晶体被称为病毒多角体或包涵体，代表病毒的感染形式。多角体在导致多角体病的两组病毒（质型多角体病毒——呼肠孤病毒科成员——和杆状病毒科）的感染周期中具有相似作用。多角体将病毒颗粒包裹在受感染细胞内的坚固晶体基质中，在释放到环境后保护病毒的感染性。被新宿主摄取后，晶体会迅速溶解，从而释放出感染性颗粒以启动新的病毒循环。由于其独特的分子结构，这些非典型感染形式长期以来一直引起病毒学家和生物化学家的兴趣。它们因其体内结晶过程以及摄取后快速释放与极端稳定性之间的反差而特别受关注。直到最近，新的方法和技术才使得通过X射线晶体学确定此类微小晶体的结构成为可能。质型多角体病毒和杆状病毒的多角体在病毒循环中具有相同作用，具有相同的立方中心对称晶格以及大小相似的称为多角体蛋白的基质蛋白。然而，它们的构建单元在多角体中的折叠和堆积方式不同。因此，这两类多角体具有不同的分子结构，并且似乎是在病毒圈中独立出现的。多角体溶解过程中酪氨酸簇的作用以及利用分子臂实现体内结晶可能代表了趋同进化的显著例子。本综述总结了我们对病毒多角体的理解，重点是最近的结构研究。我们还提供了生物技术应用的实例，这些应用需要基于结构对多角体进行工程改造，使其成为新型晶体微粒。
